Energy absorbing seat belt retractor

ABSTRACT

An energy absorbing seat belt retractor used with a seat belt assembly of a motor vehicle. The seat belt retractor includes a reel for winding and unwinding the seat belt and an elongated shaft, with the reel attached to the shaft. In one example, a movable disc is connected to and moves longitudinally along the shaft. At least one of the reel or movable disc includes a friction layer providing a friction surface such that when the movable disc is driven axially toward the reel there is frictional engagement between the reel and movable disc that absorbs impact energy on the occupant and limits the load applied to the seat belt.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a seat belt system forrestraining an occupant of a vehicle and, more particularly, to a seatbelt retractor including an energy absorbing mechanism.

2. Description of Related Art

Automobiles typically include seat belts or restraint systems forrestraining a vehicle occupant in their seat during rapid decelerationof a vehicle from a cause such as a collision. Various types of seatbelts or restraint systems using a seat belt retractor are commonlyused. One type of seat belt retractor includes a spool or reel used towind up and store the webbing of a seat belt. The spool or reel locks inplace to prevent further unwinding of the seat belt during a rapiddeceleration of a vehicle to restrain the vehicle occupant.

The retractor may include an energy absorbing mechanism such as atorsion bar that permits the spool or reel to rotate and let out anadditional amount of seat belt in response to a load placed on the seatbelt by the occupant. The forward motion of the occupant puts a load onthe torsion bar allowing the spool or reel to rotate twisting thetorsion bar whereby the restraint force on the occupant is limited byrouting the forces through the torsion bar to form said predefined seatbelt load.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides an energy absorbing seatbelt assembly used with a motor vehicle. The seat belt assembly includesa reel for winding and unwinding the seat belt and an elongated shaftwith the reel connected to the shaft. In one example, a disc connects toand rotates with the shaft; the disc is connected to the shaft in amanner wherein it can move longitudinally along the shaft. The discincludes a friction layer providing a friction surface such that whenthe disk moves axially along the shaft toward the reel there isfrictional engagement between the disc and reel.

The embodiment further includes multiple layers of friction material.Each layer formed of a different friction material having a differentcoefficient of friction; each layer may have a different shear, tensileor compressive property; each layer may have a different surface area;and each layer may have different radial and axial thicknesses resultingin a multilayer friction surface having different annularconfigurations.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided. It should be understoodthat the detailed description and specific examples, while indicatingthe preferred embodiment of the invention, are intended for illustrationonly and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective overview of a seat belt assembly incorporating aseat belt retractor according to the present invention.

FIG. 2 is a schematic perspective view of a seat belt retractor havingan energy absorbing mechanism according to the present invention.

FIG. 3 is an exploded perspective view of the seat belt retractor havingan energy absorbing mechanism as set forth in FIG. 2.

FIG. 4 is a schematic cross-sectional side view of the seat beltretractor having an energy absorbing mechanism as set forth in FIG. 2.

FIG. 5 is a side view of a portion of the energy absorbing mechanism asset forth in FIG. 2.

FIG. 6 is a partial cross-sectional view of the energy absorbingmechanism taken along lines 6-6 of FIG. 5.

FIG. 7 is a schematic end view illustrating a friction surface of theenergy absorbing mechanism as set forth in FIG. 2.

FIG. 8 is a graph illustrating an energy absorbing system for thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary and is not intended to limit the invention, its application,or uses.

FIG. 1 illustrates a seat belt system, seen generally at 10. The seatbelt system includes a seat belt retractor 12. The seat belt retractor12 typically operates to wind and unwind the seat belt 14 as the vehicleoccupant pulls out and releases the seat belt 14. It operates to take upslack in the seat belt 14; and during periods of rapid deceleration, forexample a collision, to lock and prevent extraction of the seat belt 14.As illustrated, the seat belt 14 passes through a D-ring 16 and a tongue18. The tongue 18 is freely slidable along the seat belt 14 and connectsthe seat belt 14 to a buckle 20. The end of the seat belt 14, oppositeof the retractor 12, is fixed or anchored to the base/frame of thevehicle. As illustrated, the seat belt retractor 12 is mounted to thevehicle body near the B-pillar. The foregoing description of a seat beltsystem 10 is for background only; the seat belt retractor 12 accordingto the disclosed example of the present invention can be used in othertypes of seat belt systems using seat belt retractors.

FIGS. 2-4 illustrate an example of a seat belt retractor 12 according tothe present invention including a spool or reel 22 having a cylindricalcenter portion 24 defining an axial hole or throughbore 25. A firstradially extending flange 26 is at one end of the center portion 24 anda second radially extending flange 28 is at the opposite end of thecenter portion 24. The spool or reel 22 is secured to a shaft 30extending through the axial hole or bore 25 of the spool 22. A housing32 rotatably supports the shaft 30.

The spool 22 and respective flanges 26, 28 operate to guide the seatbelt 14 during winding and unwinding of the seat belt 14. A biasingmechanism, seen generally at 34, operates to provide a retraction forceon the seat belt 14. The biasing mechanism 34 may include a torsionspring 36 connected on one end to the housing 32 and on the opposite endto the shaft 30. While shown as a torsion spring 35, the biasingmechanism 34 may also include an electric motor for rotating the spool22 in a winding or unwinding direction. As illustrated, securing thespool or reel 22 to the shaft 30 causes rotation of the shaft 30 withthe spool 22 as it winds or unwinds the seat belt 14.

As illustrated, the seat belt retractor 12 also includes an energyabsorbing mechanism, seen generally at 36. The energy absorbingmechanism 36 includes a threaded portion 38 of the shaft 30, a disc 40and a clutch or engagement mechanism, seen generally at 42, thatoperates to couple the disc 40 to the housing 32. In the disclosedexample, the clutch or engagement mechanism 42 includes a mechanical dogor pawl assembly shown as a pair of locking members 44 having guide arms53, 55 forming a channel or slot 57. As disclosed, the disc 40 ispositioned in the channel or slot 57. The locking members 44 operate toengage a plurality of gear teeth 46 on the outer peripheral edge 48 ofthe disc 40. The locking members 44 are slidably mounted for reciprocalmovement along support rods 50. Should the vehicle come to a sudden stopinertia causes the respective pendulums 52 of the locking members 44 toswing forward or rotate about the longitudinal axis of the support rods50 whereby a pawl 54 engages the gear teeth 46 on the disc 40 preventingrotation of the disc 40. Other clutch assemblies that positively coupleor connect the disc 40 to the housing 32 while enabling lateral movementalong the support rods 50 and shaft 30 are suitable. Other types ofinertia locks may also be used. Electronic clutches or lockup devicesreceiving a signal from various vehicle sensors may also positivelycouple or connect the disc 42 the housing 32.

In the disclosed example, the disc 40 includes a center aperture 56extending between the respective side surfaces 58, 60 of the disc 40.The center aperture 61 includes a plurality of threads 62 complementaryto the threaded portion 38 of the shaft 30 whereby the disc 40 isthreadably received on a threaded portion 38 of the shaft 30. The spoolor reel 22 is fixed to the shaft 30 whereby rotation of the spool orreel 22 causes rotation of the shaft 32. When the clutch mechanism 42holds the disc 40 stationary; i.e., prevents it from rotating with theshaft 38, continued rotation of the shaft 20 causes the disc 42 to moveaxially along the shaft 30 in the direction of its longitudinal axis 66,see arrows 64—FIG. 4, toward the spool or reel 22. Because the disc 40is located between the guide arms 53, 55 of the locking members 44movement of the disc 40 on the shaft 30 results in movement of thelocking members 44 axially on the respective support rods 50 in the samedirection as the disc 40. The disc 40 and locking members 44 moveaxially inward toward the spool or reel 22 at a rate and distancedetermined by the rotation of the shaft 30 and the pitch of the threadedportion 38 of the shaft 30. The shaft 30 operates as a ball screw orlead screw to move the disc 40 inward towards the spool or reel 22.

Initially the disc 40 of the energy absorbing mechanism 36 rotates withand does not move axially along the threaded portion 38 of the shaft 30.That is, the disc 40 rotates between the respective guide members 53, 55of the locking members 44 and does not move axially along the threadedportion 38 of the shaft 30 until the locking members 44 engage the disc40.

In the disclosed example a thread locking adhesive 68, see FIG. 4, isapplied to the threaded portion 38 of the shaft 30. Initially, thethreaded locking adhesive 68 maintains the disc 40 in position on thethreaded portion 38 of the shaft 30. As illustrated, the threadedlocking adhesive 68 is a thin layer of adhesive applied to the threadedportion 38 of the shaft 30. Various types of thread locking adhesivesare known and available in formulas rated to withstand variable shearforces. Thread locking adhesives offer high shear strength, goodtemperature resistance, rapid cure, easy dispensing and good vibrationresistance. Depending upon the type and corresponding shear force ofthread locking adhesive 68 the locking members 44 may engage the disc 40and prevent rotation of the spool 22 and corresponding payout of theseatbelt 14. In this manner, the seatbelt 14 can lock and restrain thevehicle occupant; however, depending upon the impact energy acting uponthe occupant when the seatbelt 14 is locked the thread locking adhesive68 may shear. When the adhesive 68 shears the spool 22 and shaft 30rotate independently of the disc 40 whereby the threaded portion 38draws the disc 40 inward into contact with the spool 22. The adhesive 68extends along a length of the threaded portion 38 and continues toabsorb energy as the disc 40 rotates on the threaded portion 38 of theshaft 30.

FIGS. 5-6 illustrate another example of frangible connection between theshaft 30 and disc 40. As used herein frangible is a structure orcomponent that yields, breaks, shears or distorts upon undergoing apredetermined load. One example is a shear member designed to shear whensubjected to a mechanical overload or impact. As with the previousexample, the disc 40 is threadably received on the threaded portion 38of the shaft 30. Both the threaded portion 38 of the shaft 30 and thethreads 62 of the center aperture 61 contain complementary grooves orchannels 70. A frangible member 72 is placed in the groove or channel70. The frangible member 72 provides a breakaway connection between theshaft 30 and disc 40. Upon reaching a desired breakaway force or shockload the frangible member 72 breaks or shears allowing relative rotationbetween the threaded portion 38 of the shaft 30 and the disc 40.Relative rotation of the shaft 30 and disc 40 results in the disc 40traveling inwardly on the threaded portion 38 of the shaft 30.

As illustrated in FIG. 6 one example of the frangible member 72 is acylindrical/pin 74 member seated in opposed semicircular grooves 76 inthe threaded portion 30 of the shaft 30 and the center aperture 61 ofthe disc 40. The seated, cylindrical/pin member 74 is designed to shearwhen the load exceeds a predetermined value. The frangible member 72 maybe formed or made from different materials including polymers, wax,metal or any other material having suitable shear strength.

A further example of a frangible connection between the shaft 30 anddisc 40 includes a polymer collar or annular member located or insertedbetween the threaded portion 38 and the threads 62 of the centeraperture 61. The polymer collar or annular member provides a relativelyconstant force or resistance to relative rotation between the shaft 30and disc 40. The frictional force between the respective threads 38, 62and collar results in an additional energy absorbing mechanism thatdampens and absorbs energy as the shaft 20 rotates relative to the disc40. The collar may include a nylon insert placed in all or part of thecenter aperture 61 of the disc 40 wherein the inner diameter (ID) isslightly smaller than the outer diameter of the threaded portion 38 ofthe shaft 30. The collar deforms elastically over the threaded portion38 of the shaft 20, but the threaded portion 38 does not cut into thematerial of the collar. The collar increases the friction between thedisc 40 and a shaft 20 and applies a compressive force against thethreaded portion 38 of the shaft 20. The collar may be formed of asuitable thermoplastic, for example nylon.

The disc 40 is threadably received on the threaded portion of the shaft30 such that it rotates with the shaft 30. However, once the lockingmembers 44 engage the disc 40, the disc 40 does not rotate about thelongitudinal axis 64 of shaft 30 but moves laterally on the shaft 30 inthe direction of the longitudinal axis 64 of the shaft 30 as the shaft30 continues to rotate. Sudden vehicle deceleration causes the lockingmembers 44 to engage and prevent rotation of the disc 40. Typically, thevehicle operator/passenger moves forward against the seatbelt during asudden vehicle deceleration causing payout of the seat belt 14 andcontinued rotation of the spool or reel 22. Continued rotation of thespool or reel 22 moves the disc 40 inwardly towards the spool or reel22.

Since the spool or reel 22 rotates but does not move laterally when thedisc 40 is driven into contact with the spool or reel 22 acertain/determinable frictional force is developed between spool or reel22 and the disc 40. In the disclosed example, the disc 40 contacts orengages a flange 28 of the spool or reel 22. As illustrated, the disc 40includes first and second layers 80, 82 of friction material on theinner or contact surface 58. The contact surface 58 of the disc 40 maycontain a first layer of friction material 80 located adjacent thecontact surface 58 of the disc 40. A second layer of friction material82 is shown placed on or adjacent the first layer of friction material80. It should be understood that additional layers of friction materialmay be placed on the contact surface 58 of the disc 40. The contactsurface 58 of the disc may also function as a friction material; forexample, the contact surface can have a roughened or configured surfacedesigned to engage a friction plate 84 located adjacent the secondflange 28 of the spool or reel 22. The friction plate 84 may alsoinclude one or more layers of friction material. FIG. 7 illustrates anexample wherein each of the first, second layers of friction material80, 82 and the contact surface 58 of the disc 40 each have an annularconfiguration with first or inner layer 80 having the smallest radial orannular width (w1) and with the remaining layer 82 and contact surface58 having a greater radial or annular width (w2, w3) increasing in astair step profile as shown in FIG. 7.

While illustrated example illustrates the disc 40 as having at least oneor more layers of friction material, this is for exemplary purposes onlyas either one of or both the disc 40 or friction plate 84 may be devoidof friction material and have an engagement surface. Both the disc 40and friction plate 84 may have one or more layers of friction material.While the layers of friction material 80, 82 of the disc 40 are formedof different materials, each having different friction coefficients andenergy absorption characteristics, the layers 80, 82 may be formed ofthe same friction material, wherein the overall surface area of each ofthe layers is varied.

Energy absorption occurs by ablation of the friction material of eachlayer. The relative hardness, wear, surface area and frictionalcoefficient of each material will cause different energy absorption andablation. Another example of the present invention includes each layerhaving different shear, tensile and compressive properties allowingdifferent amounts of energy absorption as the material wears away. Inaddition, the first layer of frictional material 80 attached to the disc40 may have a lower coefficient of friction and ablate rapidly exposingthe second layer of friction material 82. Again, the properties orcharacteristics of the various layers of friction material can bechanged or modified to achieve desired energy absorption. Further, asillustrated in FIG. 7 the greater the radial distance from thecenterline or longitudinal axis 64 the greater the distance traveled (d)and the greater the energy absorbed for a friction material. As ablationdepends in part on distance traveled, the present invention contemplatesplacing the friction materials at different distances from the center.

In another embodiment, changing the pitch of the threads 62 on thethreaded portion 38 of the shaft 20 varies the compressive force exertedby the disc 40 on the friction plate 84. The compressive force isanother parameter considered in determining the energy absorption and isanother example of a mechanism for varying the compressive force.

The present invention illustrates one example of an apparatus fordeveloping an energy absorption profile for use with a seat beltretractor. The apparatus provides multiple variable parameters any orall of which are used to achieve a force profile. In the presentexample, urging the disc 40 into engagement with the friction plate 84develops a determinable friction force between the two. As the spool orreel 22, and correspondingly the friction plate 84, turns with thepayout of the seat belt 14 the disc 40 is driven against the frictionplate 84 by rotation of the shaft 30 absorbing energy due to thefrictional force between the disc 40 and friction plate 84.

Further, the load limit or energy absorbing characteristics may beincreased by varying the material of the respective friction layers. Thefirst friction layer 80 may have a lower frictional force than thesecond friction layer 82 such that the load limit increases with eachmaterial. As the first friction 80 material is ablated, a greater forceis required for relative rotation between the disc 40 and friction plate84. Correspondingly, upon ablation of the second layer of frictionalmaterial 82, a greater force is required for relative rotation betweenthe contact surface 58 of the spool or reel 22 and the friction plate 84for relative rotation between the disc 40 in the spool or reel 22. Inthis manner, the energy absorbing retractor functions as a progressiveload limiter. In an alternative example, if the frictional force of themultiple layers decreases then the energy absorbing retractor functionsas a digressive load limiter.

Turning to FIG. 8 there is shown a Force (F) versus Time (t) graphillustrating multiple force profiles F1, F2 and F3. F1 illustrating adigressive load limiter wherein the force decreases over time. F2illustrating a progressive load limiter wherein the force increases overtime. F3 illustrating a two level progressive load limiter wherein theforce increases over time. These are examples and the force versus timeprofile need not be a straight line but may follow a curved or otherwisenonlinear profile. Varying the characteristics and parameters of theabove-identified energy absorbing mechanism 36 enables the selection anduse of a predetermined or preselected load limiting profile. Using thegeometry of the pad or material on the disc, the material itself and thecompressive force applied enables creation of virtually any force/timeprofile.

Another example of an energy absorbing mechanism 36 according to thepresent invention includes friction layers on both the friction plate 84and the disc 40. The friction plate 84 may include multiple layers offriction material at various radial distances from the longitudinal axis66 of the shaft 30. An additional example of another embodiment wouldinclude using the opposite flange 28 as the friction plate 84.

A further example includes the shaft 30 functioning as or being replacedby a torsion bar wherein as torsion bar rotates it urges the disc 40into contact with the friction plate 84. Once relative rotation betweenthe disc 40 and friction plate 84 ceases, the torsion bar twists orrotates to absorb any additional load.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A method for absorbing impact energy on a vehicleoccupant comprising the steps of: providing a seat belt retractor havinga reel for winding and unwinding a seat belt, the seat belt retractorincluding a housing, a shaft having a longitudinal axis rotatablysupported by the housing, the shaft fixed against longitudinal movementrelative to the housing, the reel secured to shaft against longitudinalmovement with respect to the shaft and rotating with the shaft;providing a movable disc, wherein at least one of said reel and movabledisc having a layer of friction material attached thereto; and movingsaid movable disc in the direction of the longitudinal axis towards saidreel wherein engagement between the reel and the movable disc absorbsimpact energy.
 2. The method for absorbing impact energy on a vehicleoccupant as set forth in claim 1 including moving said movable disctowards said reel in a manner results in a predetermined force profile.3. The method for absorbing impact energy on a vehicle occupant as setforth in claim 1 including providing the reel and the movable disc withmultiple layers of friction material, each layer having a differentcoefficient of friction whereby ablation of each layer varies energyabsorption.
 4. The method for absorbing impact energy on a vehicleoccupant as set forth in claim 1 including providing a frangibleconnection between a shaft and said movable disc.
 5. The method forabsorbing impact energy on a vehicle occupant as set forth in claim 4including a clutch mechanism wherein vehicle deceleration causesengagement between said clutch mechanism and said movable disc severssaid frangible connection whereby continued rotation of said reel movessaid movable disc toward said reel.
 6. A method for absorbing impactenergy on a vehicle occupant comprising the steps of: providing a seatbelt retractor having a reel for winding and unwinding a seat belt;providing a movable disc, wherein at least one of said reel and movabledisc having a layer of friction material attached thereto; moving saidmovable disc towards said reel in a manner such that the engagementbetween the reel and the movable disc absorbs impact energy; andproviding a frangible connection between a shaft and said movable discwherein said reel, said shaft, and said movable disc rotate together. 7.The method for absorbing impact energy on a vehicle occupant as setforth in claim 6 wherein said frangible connection includes an adhesive.8. The method for absorbing impact energy on a vehicle occupant as setforth in claim 6 wherein said frangible connection includes a pinmember.
 9. The method for absorbing impact energy on a vehicle occupantas set forth in claim 6 wherein said frangible connection includes apolymer member.
 10. A method for absorbing impact energy on a vehicleoccupant comprising the steps of: providing a seat belt retractor havinga reel for winding and unwinding a seat belt, said reel secured to androtating with a shaft; providing a disc, securing said disc to saidshaft with a frangible connection whereby said disc rotates with saidshaft; providing at least one of said reel and disc with a layer offriction material attached thereto; and severing said frangibleconnection and moving said disc towards said reel in a manner such thatthe engagement between the reel and the disc absorbs impact energy. 11.The method for absorbing impact energy on a vehicle occupant as setforth in claim 10 including using a clutch mechanism to prevent saiddisc from rotating with said shaft whereby said disc moves axially alongsaid shaft in the direction of a longitudinal axis of said shaft towardsaid reel.
 12. The method for absorbing impact energy on a vehicleoccupant as set forth in claim 10 including using a clutch mechanism toengage and prevent said disc from rotating with said shaft therebysevering said frangible connection.
 13. The method for absorbing impactenergy on a vehicle occupant as set forth in claim 10 wherein ablationof the friction material absorbs impact energy.
 14. The method forabsorbing impact energy on a vehicle occupant as set forth in claim 10wherein moving said disc towards said reel in a manner results in apredetermined force profile.
 15. The method for absorbing impact energyon the vehicle occupant as set forth in claim 10 including the step ofproviding the reel and the disc with multiple layers of frictionmaterial, each layer having a different coefficient of friction wherebyablation of each layer varies energy absorption.